Portable air supply tank



FIG. 1 is a perspective view of a portable air supply tank embodying our new design;

FIG. 2 is a left side elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a front elevational view thereof;

FIG. 6 is a top plan view thereof; and

FIG. 7 is a bottom plan view thereof. 

The ornamental design of a portable air supply tank, substantially as shown. 